Detection of the critical chloride threshold of carbon steel rebar in synthetic concrete pore solutions.

Ibrahim Gbolahan Ogunsanya,Carolyn M Hansson

doi:10.21809/rilemtechlett.2018.70

Abstract

Knowledge of the critical chloride content in concrete required to initiate corrosion of reinforcing steel is economically beneficial for the assessment and maintenance of existing structures. Also, many building codes now specify a service life of 75 – 100 years for highway bridges and the critical chloride content is an essential input parameter in the models used in design of structures. There have been numerous studies aimed at determining this parameter but there is no consensus because of the many factors influencing the corrosion. The current standard methods, e.g. ASTM G109, require many weeks or months of testing and are not appropriate for testing large numbers of specimens in different conditions. This project has demonstrated that a fairly rapid potentiodynamic polarization technique can be applied to carbon steel reinforcing bars in synthetic concrete pore solution to determine the critical value, as illustrated in the figure. The importance of selecting the appropriate synthetic concrete pore solution for this application is demonstrated by the different critical values obtained for different solutions.  The success of this test will allow the influence of different reinforcing alloys and different cementitious material mixes on the critical chloride content to be determined in a reasonable period of time.

Highlights

Chloride‐induced corrosion of reinforcing steel bars is one of the most common causes of deterioration of reinforced structure because of marine exposure and the increasing use of de‐icing and anti‐icing brines employed on reinforced structures during the harsh winter season experienced in many countries
Trendlines for the ECORR and EPIT data are extrapolated to their intersection point which, as described above, represents the chloride content of the solution at which corrosion is initiated without the application of an external stimulus, that is the chloride threshold value, CCRIT
The potentiodynamic polarization scan method of determining chloride threshold level was successful in determining the CCRIT of carbon steel rebar in three different synthetic pore solutions

Summary

Introduction

Chloride‐induced corrosion of reinforcing steel bars (rebar) is one of the most common causes of deterioration of reinforced structure because of marine exposure and the increasing use of de‐icing and anti‐icing brines employed on reinforced structures (bridges, parking lots, etc.) during the harsh winter season experienced in many countries. Chlorides diffuse through the pores of concrete structures to the reinforcement and, in sufficient quantity, they initiate active corrosion on the rebar that was initially passivated due to the high pH solution in the pores of the concrete. The amount of chlorides the steel can withstand before the initiation of active corrosion is generally referred to as the chloride threshold level or critical chloride level, Ccrit. Previous studies have employed corrosion potential monitoring, potentiostatic polarization, macrocell corrosion tests, and microcell corrosion tests. Many of these studies have been reviewed in references [2]–[4]. The decision on the methodology employed is often influenced by the time available to obtain results, but any accelerated technique has an effect on the result [5]

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Conclusion